1. The Field of the Invention
The invention relates to virtual tape server (VTS) systems and more particularly to the recovery of the association of construct definitions and logical volumes between the virtual tape server and the library manager.
2. The Relevant Art
High density, removable media storage libraries are used to provide large quantities of storage in networked computer systems. Typically, such data storage systems are employed for backup or other secondary storage purposes, but the data storage system may also be used as primary storage in circumstances that are conducive to sequential data access and the like.
The data is stored on media cartridges, such as magnetic tapes or optical disks, that are arranged in storage bins and accessed when data on a cartridge is requested. Currently available media cartridges are capable of storing much more data than the data volume units that correspond to the size of early types of media cartridges. For example, a data volume that corresponds to a 400 megabyte disk may now be stored on a tape with up to 60 gigabytes of storage capacity.
Volume mapping is used to create a correlation between the physical capacity of a storage cartridge (stacked volume or physical volume) and the data storage unit size (virtual volumes or logical volumes) of a file or block that is stored on the cartridge. Given the available data storage capacity of a single storage media, such mapping allows multiple logical volumes to be stored on a single physical volume, hence providing an efficient use of the available storage media. A virtual tape server (VTS) is one device capable of creating and maintaining such mapping among physical volumes and logical volumes.
A typical VTS system includes a virtual tape server and an automated media library. The library is controlled by a library manager that is similar to a workstation computer. Within the VTS system, typically two databases reside on separate memory disks within the system. One database resides on the virtual tape server and the other resides within the library manager.
The VTS database contains the logical-to-physical volume mapping, as well as information concerning volume attributes that define actions that were taken on a logical volume the last time it was copied to the storage media. One of the attributes included in such information is whether a secondary copy of a logical volume was made when it was last written.
The library manager database also contains attributes associated with the logical volumes stored on the media cartridges including construct names and associated attributes. The library manager database also includes a construct flag field that associates a set of construct flags with a logical volume in the library. The library manager also controls the physical loading of media cartridges in corresponding drives by storing the physical location of the physical volumes within the storage bins and controlling a robotic accessor arm that retrieves the physical volumes from the bins and loads the cartridges in the drives when a mount request is received.
Through proper management of the volume mapping, construct attributes and construct flags, a host processor and peripheral data storage equipment may access logical volumes as though they were individual physical volumes. The volume access management is provided via the virtual tape server and library manager as described above.
It is possible for the library manager database to be lost. This may happen, for instance, as the result of a hardware error or physical damage. In such an occurrence, the VTS system must be able to recover the association of the construct attributes with the corresponding logical volumes in order to resume operation of the storage management system, including accessing and appropriately processing the stored data.
Current state of the art requires that, in the case of lost data from the library manager database, the library manAger database, including any construct associations, must be fully reconstructed through physical scanning of the media cartridge labels as well as the reinsertion of logical volumes and reestablishing their associated constructs. The entire media library is made unavailable to the client during the reconstruction period. The unavailability of the media library is typically prolonged due to the quantity of volumes that must be rebuilt. Consequently, a method and apparatus are needed that are capable of recovering the association of construct definitions with logical volumes, while minimizing the length of time that the system is unavailable to the host.